Expressions of 1976-1977 and 1988-1989 regime shifts in sea-surface temperature off Southern California and Hawai'i,

Description

Sea-surface temperatures off southern California from Scripps Pier and from Koko Head, Hawai'i, were examined to determine what impact regime shifts that occurred in 1976-1977 and 1988-1989 had on environmental conditions at each location. Cumulative sums were employed to enhance the detection process. The cumulative sum time histories revealed major turning points at both locations at the time of the 1976-1977 event. At both locations, increases in temperature were indicated, consistent with the phase change in the Pacific Decadal Oscillation that took place at that time. The cumulative sums also indicated major turning points at both locations during the 1988-1989 event. A new procedure called the method of expanding means was employed to determine the long-term impact of these events. By comparing means before and after a given event it is possible to observe the magnitude of the change and to what extent it is sustained. For the 1976-1977 regime shift, temperatures increased rapidly and remained consistently higher, by ∼1°C for 2-3 yr at Scripps Pier. This increase occurred over a period of approximately 7 months and accounts for more than half of the total warming that has occurred at that location since 1920. At Koko Head, a similar response was observed with a sustained increase of approximately +0.5°C. The oceanic response to the 1988-1989 event was quite different. At Scripps Pier, temperatures before and after this event did not show any tendency to converge to significantly different values out to periods of 2-3 yr. At Koko Head, mean temperatures did converge to slightly different values after 1 yr, with mean values being consistently lower after this event (∼-0.4°C). It was shown that in some cases changes associated with these events could be identified in the original data, but without the help of cumulative sums, it is usually not possible to make a clear distinction between changes of interest and other sources of variability. Finally, decorrelation time scales for the records at both locations were estimated and found to be on the order of a year, implying spatial scales that are at least synoptic (tens to hundreds of kilometers)., Cited By (since 1996):1, ,

A curious relationship between the winds and currents at the western entrance of the Santa Barbara Channel,

Description

, , , Relationships between the surface winds and Acoustic Doppler Current Profiler (ADCP) currents at 20 levels (25 to 329 m) at the western entrance of the Santa Barbara Channel (SBC) at National Data Buoy Center (NDBC) buoy 46054 are evaluated for the 1 year period from 1 June 1996 through 31 May 1997 using a relatively new technique for correlating vectors. Gaps in the data were filled and the resulting time series examined to insure that the statistical properties of the edited data had not been significantly altered. Vertical current profiles, averaged over the year, indicate that the mean signal, although well-defined, is smaller than the variability about the mean. Vertical profiles of current speed and direction suggest the possibility of at least a twolayer system of circulation in the SBC with flow between 25 and 180 m being to the SSW and flow from 260 to 329 m being to the ENE, in agreement with previous results. Because of the existing dynamical balances, the currents are oriented approximately SW/NE, and the direction of the vertical current shear (i.e., the thermal wind) is essentially constant with depth. Thus warmer waters lie to the north and west, and colder waters,
essentially south of the buoy, are consistent with observed cyclonic circulation at the western entrance of the channel. Vector correlations over the entire year indicate that the winds and currents are poorly correlated,, ,

Sea surface temperature fronts in the California Current System from geostationary satellite observations,

Description

Sea surface temperature (SST) fronts are determined for the 2001-2004 time period from Geostationary Operational Environmental Satellites (GOES) data in the California Current System (CCS). The probability of detecting a SST front at an individual pixel location in the CCS is presented as a bi-monthly climatology. Fronts clearly indicate the seasonal evolution of coastal upwelling, as well as meanders and filaments that are often linked with irregularities in coastline geometry. Winter is characterized by low frontal activity along the entire coast. Fronts first appear close to the coast during spring, particularly south of Cape Blanco, where upwelling favorable winds are already persistent. The area of high frontal activity continues to increase during summer, especially between Monterey Bay and Cape Blanco, extending more than 300 km from the coast. The region with high frontal activity widens at ∼2.6 km day-1. Off northern Baja California, a band with persistent fronts is found close to the coast year-round, but there is no evidence of a seasonal widening of the area of higher activity. During fall, the weakening of upwelling favorable winds leads to a gradual decrease in frontal activity. An empirical orthogonal function (EOF) decomposition reveals the development of SST fronts associated with seasonal upwelling for locations north of Monterey Bay, with less summer intensification to the south. The first appearance of fronts close to the coast during spring and the occurrence of the fronts offshore later in the season are represented by additional statistically significant EOF modes. Copyright 2006 by the American Geophysical Union., , , ,

The purpose of this study is to illustrate, by example, a method called Ensemble Empirical Mode Decomposition (EEMD). Specifically, the method was used to extract the long-term trend from a time series of energy production data from the United Kingdom for the period from January 1978 through July 2011. This record is dominated by two components: an annual cycle and a long-term trend. Using EEMD, it was not difficult to extract the long-term trend. However, three components or modes from the EEMD were required to capture the underlying pattern that was the basis for the trend. This trend was also evaluated in terms of a definition for the trend given in [6]. It was found that our trend did not conform to the definition given in [6], leading to the conclusion that it is indeed a difficult problem, or perhaps impossible, to arrive at a precise definition of the trend that will be universally applicable.

Nonhydrostatic simulations of the regional circulation in the Monterey Bay area,

Description

The regional circulation in the vicinity of Monterey Bay is complex and highly variable. We use a one-way coupled, nonhydrostatic version of the Dietrich Center for Air Sea Technology (DieCAST) ocean model to simulate the regional circulation. Seasonally varying local wind stress, topographic irregularities, coastal upwelling, and forcing from the open ocean are all important in this region. Satellite imagery often shows a cyclonic eddy inside the bay and an anticyclonic eddy outside the bay. The offshore anticyclonic eddy is also associated with a year-round anticyclonic eddy over the Monterey Submarine Canyon (MSC). The offshore eddy is better organized during winter. It is found that the California Undercurrent (200-400 m) does not enter the bay itself but is diverted offshore past the entrance of the bay, presumably to reform farther north along the coast. The main branch flows northward contributing to the deep anticyclonic eddy located approximately 50 km offshore of Monterey Bay. The simulations show that vertical motion is greater during summer than winter, as expected. During spring upwelling, the deep waters often upwell along the walls of the canyon and then spread and mix with surrounding waters. The deep circulation enhances mixing significantly due to the topography. We further investigate the regional circulation by comparing it with the cases where the deep canyon was filled gradually. Vortex stretching over the canyon just beyond the entrance to Monterey Bay and along the adjacent continental slopes contributes to cyclonic circulation at deeper levels. Vertical sections of velocity along the axis of MSC indicate horizontal and vertical patterns of flow that are generally consistent with past observations on the circulation of Monterey Bay. Copyright 2007 by the American Geophysical Union., , , ,

The primary frequencies contained in the arrival sequence produced by the tsunami from the Chilean earthquake of 2010 in Monterey Bay were extracted to determine the seiche modes that were produced. Singular Spectrum Analysis (SSA) and Ensemble Empirical Mode Decomposition (EEMD) were employed to extract the primary frequencies of interest. The wave train from the Chilean tsunami lasted for at least four days due to multipath arrivals that may not have included reflections from outside the bay but most likely did include secondary undulations, and energy trapping in the form of edge waves, inside the bay. The SSA decomposition resolved oscillations with periods of 52-57, 34-35, 26-27, and 21-22 minutes, all frequencies that have been predicted and/or observed in previous studies. The EEMD decomposition detected oscillations with periods of 50-55 and 21-22 minutes. Periods in the range of 50-57 minutes varied due to measurement uncertainties but almost certainly correspond to the first longitudinal mode of oscillation for Monterey Bay, periods of 34-35 minutes correspond to the first transverse mode of oscillation that assumes a nodal line across the entrance of the bay, a period of 26- 27 minutes, although previously observed, may not represent a fundamental oscillation, and a period of 21-22 minutes has been predicted and observed previously. A period of ~37 minutes, close to the period of 34-35 minutes, was generated by the Great Alaskan Earthquake of 1964 in Monterey Bay and most likely represents the same mode of oscillation. The tsunamis associated with the Great Alaskan Earthquake and the Chilean Earthquake both entered Monterey Bay but initially arrived outside the bay from opposite directions. Unlike the Great Alaskan Earthquake, however, which excited only one resonant mode inside the bay, the Chilean Earthquake excited several modes suggesting that the asymmetric shape of the entrance to Monterey Bay was an important factor and that the directions of the incoming tsunami-generated waves were most likely different. The results from SSA and EEMD produced results that differed. Although a period of 34-35 minutes was observed in the SSA, it was not detected in the EEMD. In previous comparisons, however, we have observed that oscillations detected in EEMD were not detected in SSA. SSA also revealed an oscillation with a period of 26-27 minutes, not observed in the EEMD. This oscillation, however, may not represent a fundamental mode but instead a harmonic related to the first longitudinal mode of oscillation whose period is ~55 minutes. We conclude that both methods were useful in helping to interpret the results of this study., Cited By (since 1996):2,
Oceanography, ,

Use of acoustic tags to estimate natural mortality, spillover, and movements of lingcod (Ophiodon elongatus) in a marine reserve,

Description

Advances in electronic telemetry systems have led to fish tagging studies that are sufficiently long to provide estimates of natural mortality of many marine fishes. We used acoustic transmitters and an array of recording receivers to estimate natural mortality, residence times, and rates of movements of lingcod (Ophiodon elongatus) in a marine reserve in southeast Alaska. We surgically implanted acoustic tags in a total of 83 lingcod in December 1999 and July 2000, and distributed recording monitors with receiving ranges of at least 800 m throughout the reserve. The receivers were anchored on the seafloor in locations that resulted in overlapping receiving ranges, and thus created an array of receivers that completely encompassed an 8 km 2 reserve. In this way, we were able to estimate natural mortality rates and track movements of tagged lingcod into and out of the reserve from December 1999 through October 2001. Acoustic tag results indicated that most of the tagged fish frequently left the reserve, but were only absent for short time periods. Tagged fish showed a high degree of site fidelity. The large number of signals received from tagged fish enabled us to generate models that provided a way to predict the effects of marine reserves on yield and eggs per recruit for a cohort of female lingcod., Cited By (since 1996):8, Fish and Fisheries, ,

Comparing sea level response at Monterey, California from the 1989 Loma prieta earthquake and the 1964 great Alaskan earthquake,

Description

Two of the largest earthquakes to affect water levels in Monterey Bay in recent years were the Loma Prieta Earthquake (LPE) of 1989 with a moment magnitude of 6.9, and the Great Alaskan Earthquake (GAE) of 1964 with a moment magnitude of 9.2. In this study, we compare the sea level response of these events with a primary focus on their frequency content and how the bay affected it, itself. Singular Spectrum Analysis (SSA) was employed to extract the primary frequencies associated with each event. It is not clear how or exactly where the tsunami associated with the LPE was generated, but it occurred inside the bay and most likely began to take on the characteristics of a seiche by the time it reached the tide gauge in Monterey Harbor. Results of the SSA decomposition revealed two primary periods of oscillation, 9-10 minutes, and 31-32 minutes. The first oscillation is in agreement with the range of periods for the expected natural oscillations of Monterey Harbor, and the second oscillation is consistent with a bay-wide oscillation or seiche mode. SSA decomposition of the GAE revealed several sequences of oscillations all with a period of approximately 37 minutes, which corresponds to the predicted, and previously observed, transverse mode of oscillation for Monterey Bay. In this case, it appears that this tsunami produced quarter-wave resonance within the bay consistent with its seiche-like response. Overall, the sea level responses to the LPE and GAE differed greatly, not only because of the large difference in their magnitudes but also because the driving force in one case occurred inside the bay (LPE), and in the second, outside the bay (GAE). As a result, different modes of oscillation were excited., Cited By (since 1996):4, ,

, , , The wavelet transform is used to conduct spectral and cross-spectral analysis of daily time series of sea surface temperature (SST), surface wind stress, and sea level off the central California coast for an 18-year period from 1974 through 1991. The spectral band of primary interest is given by intraseasonal time scales ranging from 30 to 70 days. Using the wavelet transform, we examine the evolutionary behavior of the frequently observed 40–50 day oscillation originally discovered in the tropics by Madden and Julian, and explore the relative importance of atmospheric vs oceanic forcing for a range of periods where both could be important. Wavelet power spectra of each variable reveal the event-like, nonstationary nature of the intraseasonal band. Peaks in wavelet power typically last for 3–4 months and occur, on average, approximately once every 18 months. Thus, their occurrence and/or duration off central California is somewhat reduced in comparison to their presence in the tropics. Although peaks in wind stress often coincide with peaks in SST and/or sea level, no consistent relationships between the variables was initially apparent. The spectra suggest, however, that relationships between the variables, if and where they do exist, are event-dependent and thus have time scales of the same order. Cross-wavelet spectra between wind stress and SST indicate that periods of high coherence (>0.90) occur on at least six occasions over the 18-year period of record. Phase differences tend to be positive, consistent with wind forcing. For wind stress vs sea level, the cross-wavelet spectra indicate that periods of high coherence, which tend to correlate with lags close to zero, also occur, but are less frequent. As with SST, the periods of high coherence usually coincide with events in the wavelet power spectra. The somewhat weaker relationship between wind stress and sea level may be due to an independent contribution to sea level through remote forcing by the ocean originating in the tropics. Finally, simple dynamical arguments regarding the lag relationships between the variables appear to be consistent with the cross-wavelet results., ,

Development of a real-time regional ocean forecast system with application to a domain off the U.S east coast,

Description

This paper discusses the needs to establish a capability to provide real-time regional ocean forecasts and the feasibility of producing them on an operational basis. Specifically, the development of a Regional Ocean Forecast System using the Princeton Ocean Model (POM) as a prototype and its application to the East Coast of the U.S. are presented. The ocean forecasts are produced using surface forcing from the Eta model, the operational mesoscale weather prediction model at the National Centers for Environmental Prediction (NCEP). At present, the ocean forecast model, called the East Coast-Regional Ocean Forecast System (EC-ROFS) includes assimilation of sea surface temperatures from in situ and satellite data and sea surface height anomalies from satellite altimeters. Examples of forecast products, their, evaluation, problems that arose during the development of the system, and solutions to some of those problems are also discussed. Even though work is still in progress to improve the performance of EC-ROFS, it became clear that the forecast products which are generated can be used by marine forecasters if allowances for known model deficiencies are taken into account. The EC-ROFS became fully operational at NCEP in March 2002, and is the first forecast system of its type to become operational in the civil sector of the United States., Cited By (since 1996):2,
Oceanography, ,

A model for estimating cross-shore surface transport with application to the New Jersey Shelf,

Description

A one-dimensional, steady state numerical model is developed for estimating cross-shore surface transport in shallow waters, where the water depth is comparable to boundary layer thickness. The model is used to solve a momentum equation which describes the cross-shore balance. To validate the model, acoustic Doppler current profiler (ADCP) current data collected during an experiment off the New Jersey shelf in the summer of 1996 are used to estimate the cross-shore surface transport during that period and then compared with model predictions based on the local wind. The success of the model in estimating the cross-shore surface transport leads to an improved version of the conventional upwelling index (i.e., the Bakun Index), particularly for coastal areas with wide and shallow shelves, such as the east coast of the United States. Finally, the model, because of its simplicity, is well suited for operational applications where computational resources may be limited. Copyright 2010 by the American Geophysical Union., Cited By (since 1996):2, Art. No.: C04017, , , Oceanography